The present invention relates to an alfalfa seed, an alfalfa plant, an alfalfa variety, and an alfalfa hybrid which contain resistance to the potato leafhopper insect. The potato leafhopper resistance of the present invention can be incorporated into various alfalfa genetic backgrounds.
Commercial alfalfa breeders have been successful at incorporating certain types of pest resistance into high yielding alfalfa cultivars. Many newer alfalfa varieties combine resistance to several diseases, insects and nematodes. However, host plant resistance has not been available for the important alfalfa insect pests potato leafhopper (Empoasca fabae), alfalfa weevil (Hypera postica) and the Lygus bug (Lygus spp).
The potato leafhopper (PLH) is a major insect pest of alfalfa, Medicago sativa, causing significant economic losses for alfalfa producers in the Midwestern, Northeastern and Southeastern United States. This insect feeds primarily on the second and third crop cuttings each season and causes significant losses in forage yield and forage quality. Leafhopper damage is characterized by stunting of the alfalfa plant and a yellowing of the leaves which is also referred to as hopperburn. Yield losses of 40% have been reported resulting from PLH damage. Decreased protein content of the plant is also associated with PLH damage. The potato leafhopper causes more economic damage to alfalfa than any other insect or disease pest in the United States.
Until recently, breeding alfalfa for resistance to the potato leafhopper has concentrated on increased tolerance to yellowing. Although breeding progress has been made in delaying the onset of the foliar yellowing caused by insect feeding, these plant types suffer PLH induced losses in yield and quality that are similar to susceptible check varieties. The development of alfalfa varieties resistant to potato leafhopper damage has not been successful.
Several annual Medicago species have high densities of glandular hairs (GH) on leaves and stems. In various laboratory studies these GH types have shown some tolerance to potato leafhopper and/or alfalfa weevil. Attempts to cross these GH annuals with perennial alfalfa have been unsuccessful. Three perennial Medicago species have some glandular hairs on vegetative plant parts: M. prostrata, M. glutinosa and M. glandulosa. Purdue University and USDA/Kansas State University independently developed GH germplasms from these "wild" alfalfa relatives. These GH populations were made available to commercial plant breeders in the mid 1980's.
Early evaluations of the Purdue and Kansas State University GH germplasms were very disappointing. These GH germplasms had very poor vigor and were generally poorly adapted to conditions in the Midwest, including susceptibility to virtually all major alfalfa diseases.
The development of PLH resistance in alfalfa would reduce or eliminate the use of chemical pesticides to control these insects on alfalfa and would also lead to increased alfalfa yield and quality and improved environmental safety.